1. Field of Invention
The present invention relates to a plasma display device and a method for driving a plasma display panel.
2. Description of the Related Art
An AC surface discharge type panel, which is a typical plasma display panel (hereinafter, abbreviated as a “panel”) includes a front plate and a rear plate disposed opposite to each other and a plurality of discharge cells formed between these plates. The front plate includes a plurality of parallel-arranged display electrodes, each composed of a pair of a scan electrode and a sustain electrode which are formed on a front glass substrate and coated with a dielectric layer and further with a protective layer. The rear plate includes a plurality of parallel-arranged data electrodes which are formed on a rear glass substrate and coated with a dielectric layer. The rear plate further includes a plurality of barrier ribs formed on the dielectric layer in parallel with the data electrodes. The surface of the dielectric layer and side surfaces of the barrier ribs are coated with phosphor layers. The front plate and the rear plate are disposed opposite to each other in such a manner that the display electrodes three-dimensionally intersect with the data electrodes and that the discharge space between the plates is filled with a discharge gas. The display electrodes and the data electrodes intersect with each other to form discharge cells therebetween. In a panel having such a structure, a gas discharge in each discharge cell generates ultraviolet light, which excites R, G, and B phosphors for color display.
The panel can be driven by subfield methods, by which one field period is divided into a plurality of subfields, and in each subfield, each discharge cell is controlled to emit or not to emit light so as to achieve gradation display. Each subfield consists of an initialization period, a writing period, and a sustain period. In the initialization period, an initialization discharge is generated in each discharge cell so as to form a wall charge necessary for writing operation. In addition, priming (a discharge initiator=excited particles) is generated so as to reduce a discharge delay and stabilize the generation of a writing discharge. In the writing period, the scan electrodes are sequentially applied with scan pulses, and the data electrodes are applied with a write pulse corresponding to the signal of an image to be displayed. Applying the pulses in this manner allows selective writing discharges between the scan electrodes and the data electrodes, thereby forming wall charges only by selected discharge cells. In the subsequent sustain period, the sustain pulse is applied a predetermined number of times between the scan electrodes and the sustain electrodes in accordance with the display luminance. Then, only the discharge cells, which have formed wall charges by the writing discharges, are discharged to emit light. The display luminance ratio of the plurality of subfields is called “luminance weight”.
Japanese Patent Unexamined Publication No. 2000-242224 discloses several such subfield methods in order to minimize the emission irrelevant to gradation display, thereby improving the contrast ratio. One method is to generate an initialization discharge using a slowly changing voltage waveform, and another is to generate an initialization discharge only in the discharge cell in which a sustain discharge has been generated.
However, reducing the emission due to the initialization discharge irrelevant to gradation display tends to reduce the priming effect. This makes it more likely to have a discharge cell that does not emit light in spite of the application of a write pulse (hereinafter abbreviated as an “unlit cell”) when displaying low gradation levels. Such an unlit cell is caused particularly when a discharge cell to be emitted is isolated with no other discharge cells to be emitted in vicinity as in a subfield that has been subjected to an error diffusion process.